Electroless copper plating solution and process

ABSTRACT

A PLATING SOLUTION SUITABLE FOR THE ELECTROLESS DEPOSISITION OF COPPER ON FERROUS METAL SURFACES WHICH COMPRISES AN AQUEOUS ACIDIC SOLUTION CONTAINING COPPER IONS; CHLORIDE, BROMIDE, OR IODIDE IONS; A POLYALKYLENE GLYCOL; AND A DIANILINE COMPOUND OF THE STRUCTURE:   (R&#39;&#39;A,(X)B,(H2N-)PHENYL)2-R   WHEREIN R IS AN ALKYL GROUP CONTAINING FROM ABOUT 1 TO 6 CARBON ATOMS IN A STRAIGHT OR BRANCHED CHAIN; R&#39;&#39; IS AN ALKYL GROUP CONTAINING FROM ABOUT 1 TO 4 CARBON ATOMS IN A STRAIGHT OR BRTANCHED CHAIN; X IS HALOGEN; AND A IS A NUMBER FROM 0 TO 2; B IS 0 OR 1. THIS SOLUTION IS PARTICULARLY USEFUL IN FORMING AN ELECTROLESS COPPER COATING ON STEEL WIRE PRIOR TO SUBJECTING IT TO A WIRE DRAWING OPERATION.

United States Patent 3,664,852 ELECTROLESS COPPER PLATING SOLUTION AND PROCESS Kenneth J. Hacias, Detroit, Mich, assignor to Hooker Chemical Corporation, Niagara Falls, N.Y. No Drawing. Filed Dec. 30, 1969, Ser. No. 889,309 Int. Cl. C23c 3/00 US. Cl. 106-1 13 Claims ABSTRACT OF THE DISCLOSURE A plating solution suitable for the electroless deposisition of copper on ferrous metal surfaces which comprises an aqueous acidic solution containing copper ions; chloride, bromide, or iodide ions; a polyalkylene glycol; and a dianiline compound of the structure:

I b h:

R a RIB NH: N H2 This invention relates to a novel composition and process for the treatment of metal surfaces and more particularly it relates to a composition and process for the electroless copper plating of ferrous metal surfaces.

Over the years, numerous treating solutions have been proposed for forming a copper plate on metal surfaces without the use of electric current. Frequently, the solution used have been aqueous acidic solutions of inorganic copper salts, such as solutions of copper sulfate, in combination with one or more additive materials which serve to enhance the deposition of the copper plate and/or the characteristics of the plate which is produced.

While many of the compositions and processes which have heretofore been developed have been generally satisfactory, some difficulties have been encountered where different types and grades of ferrous metal surfaces have been treated. Frequently, with the compositions and processes of the prior art, variations in the type of ferrous metal being treated have resulted in similar variations in the quality of the copper coating which has been produced. Moreover, where these copper coating solutions have been used for treating steel wire, prior to wire drawing operations, it has often been found to be difficult to consistently obtain a bright, adherent coating. Additionally, the compositions of the prior art have had a relatively low tolerance for ferrous iron. With these solutions, as the quantity of ferrous iron in the bath has increased, the quality of the copper coating produced has decreased, it has, therefore, been the practice to discard the electroless copper plating solution when the ferrous iron content has built up to about 3.5 to 4% Fe and make up a new plating bath. This, of course, is costly, both from the standpoint of the cost of the treating materials as Well as in the processing time lost while the line is shut down for the building up of a new treating bath. Additionally, this frequent discarding of the bath adds greatly to waste disposal problems.

It is, therefore, an object of the present invention to provide an improved coating solution from which bright,

"ice

adherent copper coatings may be obtained on a variety of ferrous metal surfaces, without the use of electric current.

A further object of the present invention is to provide an improved process for forming a bright, adherent copper coating on a variety of ferrous metal surfaces without the use of electric current.

Another object of the present invention is to provide an improved composition and process for forming a bright, adherent copper coating on ferrous metal surfaces, which composition and process will tolerate the buildup of appreciable quantities of ferrous iron in the coating solution without adversely affecting the quality of the copper coating which is produced.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention includes an aqueous acidic solution containing copper ions; halide ions selected from chloride, bromide and iodide ions; a polyalkylene glycol; and a dianiline having the formula:

wherein R is an alkyl group containing from about 1 to 6 carbon atoms in a straight or branched chain; R is an alkyl group containing from about 1 to 4 carbon atoms in a straight or branched chain; X is halogen; and a is a number from 0 to 2; b is 0 or 1. It is found that various types of ferrous metal surfaces may be treated with this composition, without the use of electric current, to form bright, adherent copper coatings on the ferrous metal surfaces. Moreover, these results are obtained even with a ferrous iron content in the bath at the saturation point. This method is found to be particularly suited for the treatment of steel wire, prior to subjecting the wire to a drawing operation, as the copper coatings produced are found to retain their adhesion after the drawing operation.

More specifically, in the practice of the present invention, the novel plating solutions are aqueous acidic solutions containing copper ions, which solutions desirably have a pH within the range of about 0 to 2, and preferably without the range of about 0.2 to 0.4. The copper ions are desirably present in the plating solutions in amounts within the range of about 0.1 to 3.0 percent by weight of the solution and preferably in an amount within the range of about 0.3 to 0.8% by weight of this solution. The copper ions may be incorporated in the plating solutions in any suitable form, such as copper metal, and/or various copper salts. The only requirements are that What ever form of copper is used, it will produce the aqueous acidic plating solution containing the desired copper ion content, within the desired pH range, and that the ions incorporated with the copper will not have any detrimental effect on either the solution and its operation or on the quality of the copper plate which is produced.

In many instances, it has been found to be convenient to utilize copper sulfate as the source of copper ions, in forming the aqueous acidic plating solutions. Additionally, with such baths, the bath pH may be maintained within the desired range by the addition of sulfuric acid. Where the aqueous acidic plating baths used contain such sulfate ions, they are typically present in amounts within the range of about 0.1 to 30% by weight of the solution. It is to be appreciated, of course, that other copper salts may also be used as the source of copper ions, such as copper chloride, copper bromide, copper acetate, copper citrate, copper benzoate, copper metaborate, copper butyrate, copper formate, copper sulfamates, and the like, and that other acids may be used for the pH adjustment of the bath. It is to be appreciated, however, that in using such other salts or acids, particularly those containing halide ions, care should be taken that the amounts of such latter ions introduced do not exceed the maximum amounts which can be present in the solution without detrimental effect.

As has been indicated, the plating solutions of the present invention contain halide ions, selected from chloride, bromide, and iodide ions. In many instances, however, the chloride ions are preferred. Where chloride ions are used, they are desirably present in amounts within the range of about 0.001 to about 10% by weight of the solution and preferably in amounts within the range of about 0.01 to 0.5%. Where bromide ions are used, they are desirably present in amounts within the range of about 0.001 to by weight and preferably in amounts within the range of about 0.02 to 0.5% by weight of the solution, while the iodide ions, if used, are desirably present in amounts within the range of about 0.001 to 5% by weight and preferably in amounts within the range of about 0.01 to 0.2% by weight of the solution. These are desirably added as the alkali metal salts.

The polyalkylene glycol used in the plating baths of the present invention desirably has a molecular Weight in excess of about 600 and preferably has a molecular weight within the range of about 1000 to 20,000. The amount of the polyalkylene glycol in the treating solutions will vary, depending upon the particular molecular weight of the polyalkylene glycol which is used. In general, it has been found that the higher the molecular weight of the polyalkylene glycol, the lower is the concentration required to produce the desired results in the treating solution. Desirably, the polyalkylene glycol is present in the treating bath in amounts within the range of about 0.001% by weight of the solution up to its saturation concentration in the bath, with amounts within the range of about 0.006 to 1.0% by weight of the solution being preferred, the higher concentrations typically being used with the lower molecular weight materials, and vice versa. Additionally, it is to be appreciated that various polyalkylene glycols may be used, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and the like. Of these, the polyethylene glycols are generally preferred and, hence, particular reference will be made to these materials hereinafter.

The plating solutions of the present invention also contain at least one dianiline compound, having the structural formula as has been indicated hereinabove. Desirably, the dianiline compounds used will be present in amounts within the range of about 0.01% by weight of the solution up to their saturation concentration in the solution. Preferably, amounts of the dianiline compound within the range of about 0.005 to 0.1% by weight of the solution will be used.

Although various dianiline compounds, falling within the above-indicated formula may be used to give satisfactory results in the present solutions, in many instances, the preferred dianiline compound has been found to be p,p'-methylene dianiline. Accordingly, primary reference hereinafter will be made to this material. This is not, however, to be taken as a limitation on the dianiline compounds which may be used, but merely as being exemplary of these materials. Other compounds falling within the structural formula which may be used include ethylene dianiline, butylene dianiline, 4,4-methylene bis-(orthochloroaniline), and the fluoro, and bromo and iodo analogs thereof, 4,4'-methylene bis (orthomethylaniline) and the ethyl, propyl and butyl analogs thereof, and the like.

As has been indicated hereinabove, the aqueous acidic plating baths of the present invention are found to give excellent plating results even where the baths contain appreciable quantities of ferrous iron. As is recognized by those in the art, even though the baths are initially free of ferrous iron, where the baths are used to treat ferrous metal surfaces, the etching action of the bath results in the dissolution and continual buildup of ferrous iron in the plating solution. Thus, the plating baths of the present invention may also contain ferrous iron ions in amounts up to the saturation point of the ferrous iron in the bath, with amounts of ferrous iron ions within the range of about 5 to grams per liter being typical. Where such typical amounts of ferrous iron are present in the bath, and even where the ferrous iron content is greater than the saturation point of the bath, it is still found that excellent quality copper coatings can be produced.

It is to be appreciated that although certain particular preferred ranges have been given for the concentrations of the components of the plating solutions of the present invention, these concentrations are merely exemplary of those which may be used. Thus, in some instances, concentrations of these components which are outside of the ranges indicated may also be used to give satisfactory results. Accordingly, it is believed that those in the art will readily be able to determine the concentration of each of these components which should be used in each instance, depending upon the type of ferrous metal surface to be treated, the nature of the non-electrodeposited copper coating which is desired, as well as the particular type and concentration of the other components in the treating solution.

It has further been found that the combination of the various components which have been set forth hereinabove, produces an unexpectedly improved result as compared to the results obtained when all of these materials are not present in the treating solution. This has been found to be particularly true with respect to the inclusion of the halide ions, the polalkylene glycol and the dianiline components in the treating bath. Where even one of these three components is omited from the bath, it is found that it is no longer possible to consistently obtain the bright, adherent copper coating on a wide variety of ferrous metal surfaces treated, particularly with relatively large amounts of ferrous iron present. Accordingly, it is important in the present invention to include all of these components in the copper plating bath.

In carrying out the method of the present invention, the ferrous metal surface to be treated, such as a length of steel wire, is first cleaned, using any suitable cleaning techniques. Where desired, this cleaning may include acid pickling, such as with muriatic acid, alkaline cleaning, such as with alkali metal hydroxide and/ or alkali metal permanganate containing cleaners, and may include a combination of several of these cleaning or pretreating steps. Following the cleaning or pretreating of the steel surface, it is brought into contact with the copper plating bath of the present invention. Depending upon the particular configuration of the ferrous surface to be treated, various contacting techniques may be utilized such as immersion, spraying, flooding, and the like. Where the ferrous surface treated is steel wire, it has generally been found to be preferable if the wire is imersed in the copper plating bath. During the immersion of the wire in the bath, the copper plating bath of the present invention is desirably maintained at a temperature within the range of about 15 to 8-5 degrees C. and preferably 24-66 degrees C. and under these preferred conditions, immersion times of from about 10 seconds to 10 minutes are typical. After removal from the copper plating solution, the ferrous metal surface may then be rinsed with water and dried.

When the ferrous surface treated in accordance with this process is steel wire, if desired, following the application of the electroless copper plate, a suitable lubricant may be applied to the coated wire to facilitate a subsequent drawing operation. Various lubricant materials, as are known to those in the art, such as numerous soap containing compositions, may be applied to the copper plated wire and this lubricant coating then dried thereon. The wire may then be subjected to the desired drawing operation and it is found that following the drawing, the copper finish on the wire is very bright and uniform and shows good adhesion. Additionally, it is found that the solutions of the present invention may also be used to form a copper coating which is useful as a lubricant ma terial for warm forming operations, as well as a decorative copper coating.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, parts and percent are by weight and temperatures are in degrees centigrade.

EXAh IPLE 1 Four liters of an electroless copper plating solution was formulated containing 0.6% copper, as copper sulfate, 30 milliliters per liter of 6 6 degrees B. sulfuric acid, 3 grams per liter sodium chloride, A gram per liter polyethylene glycol of a molecular Weight of about 4,000 and gram per liter of p,p'-methylene dianiline. To simulate an actual operating bath, this solution was aged with steel wool until a ferrous ion content of 0.5% was obtained. The bath was then replenished with the copper sulfate and sulfuric acid to the original concentration level of these components. A 25 foot length of steel wire having a diameter of 0.064 inch was pickled for 10 minutes at room temperature in a muriatic acid pickle containing 20% muriatic acid by volume. The wire was then rinsed in cold water for 30 seconds, cleaned for minutes at about 80 degrees Centigrade in an aqueous alkali metal hydroxide-alkali metal permanganate cleaning solution. After rinsing in cold water for 30 seconds, the thus-cleaned steel wire was immersed in the copper plating bath for one minute at a temperature of about 43 degrees centigrade. After rinsing for 30 seconds in cold water the copper coated wire was then immersed for 30 seconds at a temperature of about 90 degrees centigrade in a lubricant composition containing borax, soap, and TSP and was then oven dried for 3 minutes at about 190 degrees centigrade. The wire was then drawn through two wire dies having diameters of 0.056 and 0.050 inch, respectively, and it was found that following the drawing, the copper finish on the wire was very bright and uniform and had excellent adhesion.

EXAMPLE 2 Two 4 litter copper plating solutions were made up, both containing about 0.6% Cu as copper sulfate, 30 ml./l. H 80 3 g./l. NaCl, /2 g./l. polyethylene glycol of molecular weight 4000, and about 0.6% Fe++. The Fe++ was introduced into the Ibaths by dissolving steel wool in each, then replenishing the copper and acid to their original buildup concentration. To one of the baths was added /2 g./l. of p,p-methylene dianiline. Lengths of wire were cleaned in the manner described in Example 1, processed in the two baths, then lubricated and dried as described in Example 1. The wire was then drawn through two wire dies, reducing the cross sectional area by about 20%. The wire processed in the bath containing p,p'-methylene dianiline had better adhesion after drawing than the wire processed in the bath without p,p'-methylene dianiline.

EXAMPLE 3 The procedure of Example 1 was again repeated with the exception that 4,4-methylene bis(ortho-chloroauiline) was substituted for the methylene dianiline in the copper plating solution. After processing the steel wire in the same manner as Example 1, the results obtained were found to be substantially equivalent to those obtained in Example 1.

EXAMPLE 4 A copper plating solution was formulated containing 30 ml./l. sulfuric acid, 24 grams per liter CuSO- .5lH O, 0.5% Fe++, 0.5 gram per liter p,p'-methylene dianiline, 0.5 gram per liter polyethylene glycol having a molecular weight of 4000 and 0.25 gram per liter sodium iodide. Steel wire was processed through the bath in the same manner as Example 1 and there was obtained a coating having a quality comparable to that obtained in Example 1.

EXAMPLE 5 The procedure of Example 4 was repeated with the exception that the 0.25 gram per liter sodium iodide was replaced with one gram per liter of sodium bromide and a comparable coating was obtained.

EXAMPLE 6 A copper plating solution was formulated containing 24 grams per liter CuSO .5H O, 3% sulfuric acid, 0.5% Fe++, 0.25 gram per liter p,p'-methylene dianiline, 3 grams per liter sodium chloride and 0.25 gram per liter of polyethylene glycol having a molecular weight of 20,000. Steel wire was processed through the solution in the same manner as in Example 1 and a comparable bright, adherent copper coating was obtained.

EXAMPLE 7 A copper plating solution was formulated similar to that of Example 6, but without the polyethylene glycol. Steel wire was processed through the bath both before and after adding one gram per liter of polyethylene glycol having a molecular weight of 2000. It was found that the copper coating obtained when the bath contained the polyethylene glycol was of significantly higher quality than that obtained without the polyethylene glycol.

EXAMPLES A 4 l. electroless copper plating bath was made up containing 30 ml./l. of cone. H 24 g./l. Cu SO .5H O, and 0.43% Fe++. The iron was introduced by dissolving steel wool pads in the bath. After aging, the acid and copper content were replenished to their original level. To the bath was added 20 ml. of a solution containing 20% w./v. p,p'-methylene dianiline, 20% w./v. polyethylene glycol of molecular weight 4000, and 20% v./v. muriatic acid. The bath was heated to 43 degrees C. and a length of precleaned steel wire was processed in the bath. The resulting copper coating was found to have good luster and adhesion. The bath was then aged with steel wool to a total of 10.0% iron. The copper and acid were replenished periodically to maintain their original concentration. A length of wire was again processed in the bath at this high iron concentration and the subsequent coating was of as high a quality as that obtained at the lower iron concentration.

While there have been described (various embodiments of the invention, the compositions and methods described are not intended to be taken as limiting the scope of the invention as changes therewithin are possible and each element in the following claims is intended to be understood as referring to all equivalent elements for accomplishing substantially the same result in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. An aqueous acidic solution suitable for forming a copper plate on ferrous metal surfaces without the application of electric current which comprises copper ions in an amount from 0.1 to 30% by weight, halide ions in an amount within the range of 0.001 to 10% by weight, wherein the halide ions are independently selected from the group consisting of chloride, bromide, and iodide; a polyalkylene glycol present in an amount of at least about 0.001% by weight and having a molecular weight within a range of about 600 to 20,000; and a dianiline com- 7 pound present in an amount of at least about 0.01% by weight to saturation, having the formula:

NH: N H:

wherein R is an alkyl group containing from about 1 to about 6 carbon atoms in a straight or branched chain; R is an alkyl group containing from about 1 to 4 carbon atoms in a straight or branched chain; X is halogen; a is a number from to 2; and b is 0 or 1.

2. The solution as claimed in claim 1 wherein the halide ions are chloride ions.

3. The solution of claim 1 wherein the polyalkylene glycol is polyethylene glycol.

4. An aqueous acidic solution suitable for forming a copper plate on ferrous metal surfaces without the application of electric current which comprises copper ions in an amount from 0.1 to 30% by weight, halide ions in an amount from the range of 0.001 to by weight, wherein the halide ions are independently selected from the group consisting of chloride, bromide, and iodide; a polyalkylene glycol present in an amount of at least about 0.001% by weight and having a molecular weight within a range of about 600 to 20,000; and p,p'-methylene dianiline in an amount from about 0.01% by weight to saturation.

5. The solution of claim 1 wherein the alkylene of the polyalkylene glycol has from 2 to 4 carbon atoms.

6. A process for forming a copper coating on ferrous surface to be coated with the coating composition as claimed in claim 1 and maintaining this composition in contact with the ferrous metal surface for a period sufficient to effect the formation of a copper coating.

7. The process as claimed in claim 6 wherein th halide ions are chloride ions.

8. The process of claim 6 wherein the polyalkylene glycol is polyethylene glycol.

9. The process of claim 6 wherein the alkylene of the polyalkylene glycol has from 2 to 4 carbon atoms.

10. The solution of claim 4 wherein the alkylene of the polyalkylene glycol has from 2 to 4 carbon atoms.

11. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim 6.

12. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim 8.

13. The process of claim 6 wherein the dianiline compound is p,p'-methy1ene dianiline.

References Cited UNITED STATES PATENTS 2,049,517 8/1936 Saukaitis 13441 2,217,921 10/1940 Saukaitis 106-1 3,141,780 7/1964 Simon et al. 106-1 LORENZO B. HAYES, Primary Examiner U.S.Cl. X.R. 117130 E, R 

